Vending machines and coin handling apparatus

ABSTRACT

An electrical discharge produces an acoustic impulse, and a reflection of the impulse from the upper coin in a coin stack is sensed so that the level of the coin stack can be determined from the time taken for the reflection to be received. Alternatively, or additionally, the acoustic impulse can be used to detect coin jams, the presence and/or width of a coin store, the state of a coin routing gate or the quantity of a vendible product.

[0001] This invention relates to vending machines and coin handlingapparatus, such as may incorporatevalidators.

[0002] Certain aspects of the invention are of particular relevance tovending machines.

[0003] Vending machines typically have to been visited frequently by arouteperson to check that none of the stock items has run out. Thevisits need to be frequent enough to prevent stock items from runningout, resulting in lost sales, but not so frequent as to result inunnecessary effort. This can be difficult to plan, especially as therate at which items are sold can vary.

[0004] Vending machines can develop faults whereby a product which isintended to be vended becomes jammed, and therefore a customer who haspaid for an item may find that he does not receive that item. To avoidthis consequent loss, it is known to provide vending machines withsensors which determine whether a product has been vended as intended.It is also known to provide a sensor which detects when a product hasrun out, and in response thereto to inhibit further vends.

[0005] According to an aspect of the present invention, there isprovided a vending machine which has means for measuring a quantity of avendible product stored therein. Such an arrangement can be used formultiple purposes. It is possible to determine whether the quantity ofthe vendible product changes following an intended vend, thereby toconfirm that the vend has taken place. If the sensed quantity does notchange appropriately, the machine can be caused to attempt again to vendthe product, in the hope of clearing a fault or jam. It is furtherpossible to ensure that vends are inhibited if the level is determinedto be zero. In a preferred aspect of the invention, however, a signalrepresenting the sensed quantity is transmitted to a remote location, sothat it is possible to determine, before a product has run out, thatreplenishment will soon be required, and a visit from a routeperson canthan be arranged.

[0006] Although this aspect has been described in the context ofmeasuring the quantity of products available for vending (and theseproducts could be of any type, such as packages, cups, cans, or bulkitems of liquid or granular solid), similar advantages can apply to useof the technique for measuring waste products, such as liquid overspillin a waste container, as the techniques will provide advance warning ofwhen a routeperson is required. Another alternative is to measure thequantity of an item being vended (such as liquid in a cup), so as toobtain a more accurate vend than is achieved simply by, e.g. a timingoperation.

[0007] Various techniques can be used to determine the quantity of avendible product. However, there is one particularly preferredtechnique, which is relatively cheap to implement and which is suitedfor use with many different physical configurations. Consequently,according to a preferred embodiment of the invention, the quantity of avendible product is determined by generating an acoustic impulse anddetermining the time taken for a reflection of the impulse from asurface to reach a receiver. As described below, a technique like thishas previously been described (in GB-A-2190749) for measuring thequantity of coins in a storage tube. There is further explained below aparticularly advantageous improvement which has been applied to thetechnique, and which is of benefit when used in a vending machineaccording to the present aspect of the invention.

[0008] Other aspects of the invention are of particular relevance tocoin validators.

[0009] Coin validators commonly include many sensors, for example fordetecting the properties of inserted coins, detecting the presence ofcoins at various locations within the coin path, detecting the level ofcoins within coin stores, etc. Many attempts have been made to producesensors which are more effective, more compact and/or less expensive.

[0010] One example is shown in GB-A-2190749. The disclosed arrangementmonitors the level of coins within a coin tube by directing a train ofultrasonic pulses towards the top of the stack and measuring the timebetween the emitted and reflected pulses. Such an arrangement has theadvantage of providing an indication of the absolute level of coins,rather than merely an indication of whether or not the level hasexceeded a certain threshold, as is the case with many common levelsensors. However, the described arrangement suffers from a number ofdisadvantages. It is difficult to construct, because the ultrasonictransducer is a resonant structure and therefore produces ringing. Anydamping used to reduce this ringing will also reduce the power output,leading to potential noise problems. Furthermore, if a substantialproportion of the transducer output is coupled into the surroundingstructure, this can result in saturation of the receiving microphone.The transducer has to be spaced by a large distance from the stack ofcoins, because otherwise the microprocessor will detect the reflectedpulse before it has ceased detecting the emitted pulse, so that theoverall structure is large, in addition to being difficult to assemble.

[0011] It would be desirable to mitigate at least some of theseproblems.

[0012] It would be desirable in addition to provide simple andcost-effective techniques for detecting various aspects of theconfiguration of a coin validator, so that faults and jams can be sensedor avoided.

[0013] According to a further aspect of the invention, a coin handlingapparatus is provided with an electric spark generator. In order todetect the location or presence of a surface, the spark generator isactuated to produce a pressure wave, and the time taken for the pressurewave to reach a receiver is detected.

[0014] In the embodiments described below, the pressure wave isreflected from the surface (assuming the latter is present) to amicrophone. The sensing of the reflection by the microphone provides anindication of the presence of the surface and the transit time providesan indication of the location of the surface. The spark generates apowerful pressure wave with a very steep rise-time and a very briefduration. The steep rise time provides a very accurate result ascompared with, for example, the arrangement of GB-A-2190749, in whichthe relatively shallow rise time means that the calculation of thesurface location from the sensing of the reflected pulse will beamplitude dependent and therefore inaccurate. The short duration of thepulse allows the spark generator to be located close to the surfacebeing detected without running the risk of the emitted pressure wavebeing detected contemporaneously with the reflected wave.

[0015] Other aspects of the invention are directed to the idea of usingacoustic impulses for detecting the configuration of a coin validator;thus, for example, an acoustic impulse can be used to detect whether ornot a coin store is present or whether or not a coin routing gate is ina predetermined position, by determining whether the reflected acousticimpulse is received within a particular time period. An acoustic impulsecould also be used for detecting a dimension of a coin store (forexample the width of a coin tube) by sensing how long it takes for theimpulse to reach the receiver after having been reflected off a wall ofthe store. The presence of a jammed coin in a particular orientationwill also be detected as a result of interference with the acousticimpulse. All these possibilities are made more practicable by the use ofparticularly short impulses, preferably less than 100 microsecond andmore preferably less than 25 microseconds, such as may be generated byan electric spark.

[0016] Various embodiments of the invention will now be described by wayof example with reference to the accompanying drawings, in which:

[0017]FIG. 1 schematically shows a coin handling apparatus in accordancewith the invention;

[0018]FIG. 2 is a schematic view of a coin tube of the apparatus of FIG.1, which has associated therewith a level sensor operating in accordancewith a method of the present invention;

[0019]FIGS. 3a and 3 b are diagrams of a circuit for operating the levelsensor;

[0020]FIG. 4 is a diagram of waveforms appearing in the circuit of FIGS.3a and 3 b;

[0021]FIG. 5 is a perspective view of a coin storage section of theapparatus of FIG. 1;

[0022]FIGS. 6a and 6 b are schematic diagrams showing variousconfigurations of a coin validator that could be detected using thetechniques of the present invention;

[0023]FIG. 7 is a schematic view of a vending machine according to theinvention; and

[0024]FIG. 8 is a plan view of a product dispenser in another vendingmachine according to the invention.

[0025] Referring to FIG. 1, a coin handling apparatus 102 includes acoin validator 104 for receiving coins as indicated at 106. During thepassage of the coins 106 along a path 108 in the validator 104, thevalidator provides signals indicating whether the coins are acceptable,and if so the denomination of the coins.

[0026] Acceptable coins then enter a coin separator 110, which has anumber of gates (not shown) controlled by the circuitry of the apparatusfor selectively diverting the coins from a main path 112 into any of anumber of further paths 114, 116, 118, 119 and 120, or allowing thecoins to proceed along the path 112 to a path 122 leading to a cashbox124. If the coins are unacceptable, instead of entering the separator110 they are led straight to a reject slot via a path 126.

[0027] Each of the paths 114, 116, 118, 119 and 120 leads to arespective one of five coin tubes or containers 128, 130, 131, 132 and134. Each of these containers is arranged to store a vertical stack ofcoins of a particular denomination. Although five containers are shown,any number may be provided.

[0028] A dispenser indicated schematically at 136 is operable todispense coins from selected ones of the containers when change is to begiven by the apparatus.

[0029] Referring to FIG. 2, this shows a representative coin tube 2corresponding to any one of the containers 128, 130, 131, 132 and 134.The coin tube 2 has stored therein coins 4 in a face-to-face verticalstack, resting on a base the level of which is indicated by datum line6. An acoustic impulse generator, in the form of a spark gap 8, and amicrophone 10, are located above the coin tube 2. In this embodiment,both the spark gap 8 and the microphone 10 are located on a sensor datum12 located at a height H above the base 6 of the coin stack (although itwould be possible for them to be mounted at different heights).

[0030] In order to detect the level of coins in the tube 2, a controlcircuit causes the triggering of a spark, and the time taken for theresulting acoustic impulse to be reflected off the uppermost coin in thestack 4 and travel to the microphone 10 is measured. Assuming that thetime taken is t, and the speed of sound is V, then the stack height isgiven by S=H−Vt/2.

[0031] V=331.29×{square root}(T/273) m/s, where T is the absolutetemperature. Accurate results can be obtained by assuming an averagetemperature; however, in the preferred embodiment, a temperature sensoris used to provide even greater accuracy. This assumes that the height His known to sufficient accuracy, which can be achieved either by controlof manufacturing tolerances, or by an initial calibration operation inwhich the reflection time t is measured with the coin tube empty andthen H is calculated to be equal to Vt/2.

[0032] Referring to FIG. 3a, an oscillator 20 is coupled to an invertertransformer 22. The output of this is rectified by a diode 24 and the DCoutput stored on a capacitor 26, providing approximately 250 volts DC.This voltage is coupled, via a thyristor 28, across a step uptransformer 30. Upon triggering of the thyristor 28, a voltage ofapproximately 9 kV is generated at the output of step up transformer 30,which is connected across the spark gap 8. This produces a powerfulspark having a rise time of less than 20 microseconds. The power of thespark is coupled directly to the air, rather than to the surroundingstructure, thus resulting in a very efficient and brief acousticimpulse.

[0033] The thyristor is triggered at regular intervals, e.g. 50 Hz, by aspark rate generator 36, which is coupled to the thyristor by an opticalinterface including an LED 38.

[0034] The spark rate generator 36 also has an output A which isdelivered to the detection circuit shown in FIG. 3b. This output Acarries a single pulse each time a spark is generated. This pulse isapplied to a start input 39 to start a counter 40.

[0035] The output of the microphone 10 is delivered through an amplifier42 to a comparator 44. The comparator output rises whenever themicrophone detects a sufficiently loud signal, such that the amplifieroutput exceeds a threshold V_(REF). The rising comparator output isapplied, via an AND gate 46 to a stop input 48 of the counter 40. Theclock input 49 of the counter 40 is coupled to a 10 MHz clock 50.Accordingly, the counter counts for the time between the spark beinggenerated and the reflected impulse being received by the microphone 10.A processor 52 takes the output of the counter 40, and the output of atemperature sensor 54, in order to calculate the stack height S. Thetemperature sensor 54 could be a discrete sensor, e.g. a thermistor, orcould be an output derived from a sensor used for other purposes, e.g.an electromagnetic sensor used to measure coin properties, in which casethe sensor output when no coin is present could be used to indicatetemperature.

[0036] Referring additionally to FIG. 4, the waveform A represents thepulse sent to the counter 40 by the spark rate generator 36. Waveform Bshows the output of the comparator 42. It will be noted that themicrophone detects pulses at around the time the spark is generated. Themicrophone will directly detect the acoustic impulse from the spark gap.Also, because the spark is so powerful, it will create a degree ofringing in the associated structure, even though a very small proportionof the power is coupled to the structure. This may create one or moreadditional vibrations which are picked up by the microphone 10.

[0037] In order to stop these initial pulses from interfering with theoperation of the counter 40, a delay circuit 56 is provided to generatea blanking pulse shown at C in FIG. 4. This lasts for approximately 150microseconds from the beginning of the spark trigger pulse shown at A inFIG. 4, and is sufficiently long to encompass any of the initial pulsessensed by the microphone. The pulse C is applied by an inverter 58 toanother input of the AND gate 46, so that no output from the comparator44 is transferred to the stop input of the counter while the blankingpulse C exists.

[0038] In a modified arrangement, the circuit is operable to take twotime measurements, t1 and t2, which as indicated in FIG. 4 representrespectively the first acoustic impulse I1 detected after the sparkpulse has been emitted, and the first acoustic impulse I2 detected aftera predetermined blanking period, which can correspond to the period C ofFIG. 4. There is a predetermined, known distance D associated with thefirst of these impulses, I1. For example, this may be the distancebetween the spark generator 8 and the microphone 10. Alternatively,there may be a reflective surface at a fixed, known position, thedistance D being the sum of the distance from the spark generator to thereflective surface and from the reflective surface to the microphone.

[0039] Using such an arrangement, the coin level can be calculated bydetermining the distance L from the spark generator to the top of thecoin stack and then from the top of the stack to the receiver, using therelationship: L/D=t2/t1.

[0040] This provides an accurate indication of level without requiring atemperature measurement, because temperature influences effect t1 and t2correspondingly and therefore cancel out.

[0041] The need to know the dimension D can be avoided by appropriatecalibration operations.

[0042] In the arrangements described above, instead of calculating theposition of the top of the stack, the position can be determined by useof a look-up table addressed using the time measurement or measurements.

[0043] The spark generator may be continuously activated at a desiredrate throughout a period when measurements are being made. In order toimprove resolution, the processor 52 preferably takes a plurality ofmeasurements from the counter 40 and averages them.

[0044] Alternatively or additionally, the spark rate generator 36 may beresponsive to a signal from a validation circuit (not shown) whichindicates that a coin is being routed to the coin store 2. In responseto this, a first spark is generated in order to measure the level ofcoins in the tube and, at a predetermined delay period later, a secondspark is generated to take a further measurement. These measurements arecompared, and if the difference does not represent an additionalthickness corresponding to a single coin, an error signal is generated.Alternatively, or additionally, measurements made before and after acoin dispensing operation could be compared. In these embodiments, themeasurements are event-driven.

[0045] In a preferred version of the event-driven embodiments, the sparkrate generator 36 enabled for a predetermined period each time ameasurement is made. This enables a plurality of readings to be takenand averaged to form each measurement.

[0046] Experiments suggest that, assuming a coin set wherein thethinnest coin has a thickness of 1.75 mm, assuming no temperaturecompensation is used and there is a possible 10° C. variation intemperature, it is possible to obtain an accuracy which corresponds tohalf the thickness of a coin (with a level of 29 coins). However, theerror is effectively eliminated by temperature compensation. In apractical arrangement, it is possible, without undue effort, to confinevariations due to mechanical tolerances to 25% of the thickness of thethinnest coin. It is also found that because of the fast rise time ofthe acoustic impulse, it is possible to measure a reflection time to 0.1microseconds resolution. By averaging 10 readings, it is found that aresolution equating to approximately 0.18 mm is obtained.

[0047] Accordingly, using the teachings of the invention, a measurementresolution which is better than the thickness of a single coin isreadily achievable. This compares with the arrangement in GB-A-2190749,in which experiments suggest that the rise time of the acoustic impulseis likely to be of the order of 250 microseconds, and the overall timeof the impulse possibly in the order of 1.5 milliseconds. Furthermore,if the transducer is damped to reduce the pulse width sufficiently, thepower of the impulse is so low that noise problems present themselves.Accordingly, for practical purposes the resolution of a single coinwould be very difficult, if not impossible, to achieve.

[0048]FIG. 5 illustrates a practical arrangement which operates inaccordance with the teachings of the present invention. In this case,there is a single spark generator 8 for generating acoustic impulses fordetecting the stack levels in all of the containers 128, 130, 131, 132and 134. The acoustic impulses are conveyed to the containers using amanifold 60. The spark generator 8 has terminals 62 and 64 leading to apair of wires (not shown) whose ends are separated by approximately 3millimetres. The manifold 80 comprises 3 millimetre diameter tubesextending from the spark region to locations above the containers. Theend of each tube is flared to increase the internal diameter from 3millimetres to 6 millimetres, providing improved impedance matching andacoustic impulse transmission characteristics. Each flared end 66 islocated immediately adjacent a respective microphone 68, with the centreline between the flared end 66 and the microphone 68 being located overthe centre of the respective one of the containers 128, 130, 131, 132and 134. This helps to avoid unwanted acoustic reflections.

[0049] The use of the manifold 60 for conveying the acoustic impulse torespective areas has been found to reduce significantly the cost of andspace occupied by the device according to the present invention. Themicrophones can be successively switched into and out of circuit so thatthe same detection arrangement can be used for all of the level sensors.

[0050] Referring again to FIG. 1, each of the containers 128, 130, 131,132 and 134 is preferably removable and replaceable by a container ofdifferent diameter. The containers may, if desired, be located in asingle cassette which is itself removable from the apparatus 102 tofacilitate removal and replacement of individual containers.

[0051] Preferably the mounting arrangements for the individualcontainers are such that the centre of the top of each container isalways located at a predetermined position, irrespective of the diameterof the container. Thus, if for example the container 128 were to bereplaced by a container of different diameter, as indicated at 129 inbroken lines, the container, the end 66 of the manifold and themicrophone 68 would still have the appropriate relative positions forcorrect operation.

[0052] As explained further below, it is possible to apply thetechniques of the invention for detecting parameters other than thelevel of coins in a coin tube. It has been determined that similartechniques can be used to advantage for other purposes, and that this ismade particularly practicable if it is possible to produce acousticimpulses which have a very fast rise time and short duration, becausethis enables the fitting of the detector into a compact coin validator.Accordingly, an electrical arc discharge arrangement such as thatmentioned above is particularly desirable. However, it may be possibleto use other arrangements, for example, a damped piezoelectrictransducer which is energised by a brief, high voltage, although it isenvisaged that this would be significantly more difficult to achieve.

[0053] Separate acoustic impulse generators may be provided fordifferent purposes in the coin validator. However, in a particularlypreferred embodiment of the invention, generated acoustic impulses areused for multiple purposes. This could be achieved by having severaldifferent microphones at predetermined positions so as to detectrespective reflections from respective surfaces. Alternatively, as inthe arrangement described in the following paragraph, the same generatorand microphone can be used for more than one purpose, given a suitablearrangement for analysing the output of the detecting circuitry.

[0054] Referring again to FIG. 2, the invention could be used fordetecting a coin jam. For example, if a coin is jammed in the positionshown in phantom at 18, the reflected impulse from the spark gap may bedirected away from the microphone, possibly into the side wall of thecoin tube. Alternatively, the reflection may have reached the microphoneduring the blanking period shown at C in FIG. 4. Therefore, in thepreferred embodiment, in order to detect such a jam, the processor 52 isarranged to determine when the count reached by the counter 40 exceeds aparticular threshold, which indicates that no appropriate reflection hasbeen received by the microphone. In response thereto, the processorgenerates an error signal.

[0055] A similar effect is produced also if the coin tube 2 is notpresent. Accordingly, even if there is no possibility of a jam in thecoin tube, the processor may be arranged to generate an error signal ifno reflected impulse is sensed by the microphone within a predeterminedinterval following the generation of the spark.

[0056] Referring to FIG. 6a, an acoustic signal may also be used todetermine whether a gate 80 is in a first position, in which it projectsinto a channel 82 forming a coin path, or whether the gate has beenwithdrawn behind the rear wall 84 of the path.

[0057] Referring to FIG. 6b, an acoustic impulse may also be used todetermine the width of a coin tube 2, possibly by reflecting theacoustic impulse off an upwardly projecting extension 90 of the tube.This procedure could be used for automatically configuring the coinvalidator so that coins of the correct size are directed to that cointube. In these circumstances the same sensor may be used to detect thepresence of the coin tube, or of a cassette containing this and othercoin tubes.

[0058] The techniques of the invention could also be used fordetermining the level of coins in a cashbox, even when these aredisposed in a disordered manner. In these circumstances, it may bedesirable to use two or more level sensors, and/or the arrangement maybe such that the sensor is intended to indicate only when the levelexceeds the predetermined threshold.

[0059] It should be noted that the techniques of the invention could beused exclusively for purposes other than coin level sensing.

[0060] Referring to FIG. 7, this shows schematically a vending machine500 in accordance with the invention. The vending machine 500 is a hotdrinks dispenser. A cup store 502 stores cups in a stack 504, from whichthe botommost cup can be delivered to a filling compartment 506, asindicated at 508. Hot water is then fed to the cup 508 via a spout 510.Any spilled liquid drains into an overspill container 512.

[0061] The machine has three pairs of acoustic impulsetransmitter/receivers 8, 10 forming respective level sensors, allcoupled to a central controller 514. Each is structured like the levelsensor of FIG. 2. The controller 514 includes a control circuit likethat of FIGS. 3a and 3 b, and is arranged to couple the control circuitto each level sensor in turn.

[0062] The level sensors are arranged to measure (a) the number of cupsin the cup store 502, (b) the level of liquid dispensed into a cup 508and (c) the level of liquid in the overspill container 512. Thecontroller is coupled to a modem 516, which is itself connected to asocket 518 for receiving a standard telephone cable. The arrangement issuch that whenever the measured level of the cups in the store 502 fallsbelow a predetermined level, and whenever the level in the overspillcontainer 512 exceeds a predetermined level, the controller 514 uses themodem 516 to communicate with a remote location to advise that servicingwill soon be required. As an alternative, the remote location can bearranged to poll the vending machine regularly, to determine the levelsin the cup store 502 and the overspill container 512.

[0063] The controller 514 is arranged to terminate the dispensing ofliquid to the cup 508 if the level of the liquid therein exceeds apredetermined value.

[0064] The cups may be pre-filled with appropriate ingredients.Alternatively, there may be a separate store for the ingredients, inwhich case a further level sensor may be provided for this store.

[0065] It is not necessary for all these sensors to be provided. If morethan one sensor is provided, it may be possible for them to use a commonacoustic pulse generator 8. Although it is desirable for the sensors touse electric arc discharges to produce the acoustic impulse, this is notessential, especially if more room is available and/or less accuracy isrequired.

[0066]FIG. 8 shows a product dispenser 600 of a further vending machineaccording to the invention. This is of generally known form, whereinindividual products 602 are disposed in respective turns of a helicalstructure 604. By rotating the helical structure 604 once about itsaxis, all products are moved towards an aperture 606, and the endmostproduct falls out of the structure into the aperture.

[0067] A level sensor incorporating an electric arc discharge device 8and a receiver 10 are provided. The acoustic impulse from the arctravels along the axis of the helical structure 604, and is reflected tothe receiver 10 by the last product held in the structure, so the timeof receipt of the reflected impulse represents the number of productsstored in the helix. This arrangement can be controlled and used as thearrangements described above.

[0068] In the arrangements of FIGS. 7 and 8, if it is detected that thelevel of cups or products has decreased to zero, further vending isinhibited, and if it is detected that the level has not decreasedappropriately after a vend has been instructed, a further attempt at avend is made.

1. A method for detecting the presence and/or location of a surface in acoin handling apparatus by detecting an acoustic pulse reflected fromthe surface, characterised in that the acoustic pulse is produced by anelectric discharge.
 2. A method as claimed in claim 1, including thestep of producing a value representative of the location of the surfaceby determining the time taken for receipt of the impulse.
 3. A method asclaimed in claim 2, wherein the value is representative of the number ofcoins in a coin store.
 4. A method as claimed in claim 3, wherein thecoin store is a tube in which the coins are stored face-to-face in astack.
 5. A method as claimed in claim 3, wherein the store is acashbox.
 6. A method as claimed in any one of claims 2 to 5, includingthe step of additionally detecting the time taken for the acoustic pulseto travel a predetermined distance, and determining said value independence on the relationship between the detected times.
 7. A methodas claimed in any preceding claim, including providing a signalindicating whether or not the surface has been detected.
 8. A method ofdetecting the configuration of a coin passage in a coin validator, themethod comprising generating an acoustic impulse and determining theconfiguration from the time taken for a reflection of the impulse from asurface of the passage to reach a receiver.
 9. A method as claimed inclaim 8, wherein the acoustic impulse has a duration of less than 100microseconds.
 10. A method as claimed in claim 8 or claim 9, wherein theacoustic impulse is produced by an electrical discharge.
 11. A method asclaimed in any preceding claim, comprising the step of producing asignal indicating a coin jam in dependence upon the output of thereceiver.
 12. A method as claimed in claim 11, wherein the signalrepresenting the coin jam is produced if the receiver does not producean output which exceeds a predetermined threshold within a predeterminedperiod.
 13. A method as claimed in any preceding claim, including thestep of providing a signal indicative of the presence of a coin store independence on the output of the receiver.
 14. A method as claimed in anypreceding claim, including the step of producing an output representingthe position of a coin routing gate in dependence on the output of thereceiver.
 15. A method as claimed in any preceding claim, includingproducing a signal representing the size of a coin store in dependenceon the output of the receiver.
 16. A method as claimed in any precedingclaim, including the step of detecting the ambient temperature anddetermining the location of a surface reflecting the acoustic impulsetaking into account the time taken for the reflection to reach thereceiver and the temperature.
 17. A method as claimed in any precedingclaim, including the step of repeatedly generating acoustic impulses andaveraging the detected times.
 18. A method as claimed in any precedingclaim, including generating the acoustic impulse in response to acontrol signal representative of a detected event.
 19. A method asclaimed in claim 18, including the step of generating first and secondacoustic impulses in response to a signal representing that a coin hasbeen routed to a coin store, and determining whether the response of thereceiver to the acoustic impulses differs in a way which indicates thatthe coin has been received in the coin store.
 20. A coin handlingapparatus having means for performing a method as claimed in anypreceding claim.
 21. Coin handling apparatus having a coin store and alevel detector for detecting the level of coins in the store, the leveldetector comprising means for generating an electric discharge and meansfor determining the level from the time at which an acoustic impulseproduced by the electric discharge is determined to have been reflectedby a surface whose location is indicative of the level.
 22. Apparatus asclaimed in claim 21, wherein the store is a coin tube in which the coinsare stored in a stack, the apparatus having mounting means forsupporting the coin tube in such a way as to allow replacement of thecoin tube by a tube for accommodating coins of different diameter, themounting means being such as to cause the centre of the tube mouth tohave a predetermined location irrespective of which tube is supportedthereby.
 23. Apparatus as claimed in claim 21 or 22, having a pluralityof coin stores and a manifold for directing acoustic impulses from theelectric discharge generating means to the respective stores to enabledetection of the levels of coins in the stores.
 24. Apparatus as claimedin claim 23, wherein the manifold has outwardly-flared ends for emittingacoustic impulses into the respective stores.
 25. A method for detectingthe quantity of a vendible product in a vending machine, the methodcomprising detecting the time taken for an acoustic pulse to reach areceiver.
 26. A method as claimed in claim 25, wherein the acousticpulse has a duration of less than 100 microseconds.
 27. A method asclaimed in claim 25 or claim 26, wherein the acoustic pulse is producedby an electrical discharge.
 28. A method as claimed in any one of claims25 to 27, including the step of detecting the ambient temperature anddetermining the location of a surface reflecting the acoustic impulsetaking into account the time taken for the reflection to reach thereceiver and the temperature.
 29. A vending machine having means forperforming a method as claimed in any one of claims 25 to
 28. 30. Avending machine having means for detecting the quantity of a vendibleproduct stored therein.
 31. A vending machine as claimed in claim 30,wherein the detecting means is operable to determine the quantity bymeasuring the amount of time taken for an acoustic impulse reflectedfrom a surface to be detected.
 32. A vending machine as claimed in claim31, wherein the detecting means comprises means for producing anelectric arc discharge for generating the acoustic impulse.
 33. Avending machine as claimed in any one of claims 30 to 32, includingmeans for transmitting an indication of said detected quantity to aremote location.